With the detection and isolation of microbes in samples from oil reservoirs, researchers found out that not all microbes in oil reservoirs are harmful to oil exploitation, the metabolism products and activity of some microbes in oil reservoirs can be use to enhance oil recovery. Therefore, microbial enhanced oil recovery (MEOR) was proposed and implemented as one of tertiary measures to enhance oil recovery.
The principal part of MEOR is potential microbes. According to studies of functional microbes for MEOR, strains of Bacillus are documented as a functional group of microbes for MEOR. Bacillus is able to produce biosurfactant that can lower interfacial tension between crude oil and aqueous liquid and rocks, so as to improve the mobility of the crude oil and significantly increase the production of the oil; Bacillus can increase the production of the oil by degrading long chain hydrocarbons to decrease viscosity of crude oil and to improve the mobility of crude oil; Bacillus can also increase the production of the oil by producing polymer to selectively plug in oil reservoirs, so as to promote the volumetric sweep efficiency of injected water.
For studies and field trials of MEOR, investigating microbes inhabiting in oil reservoirs is a key and primary step to discover potential microbes and design strategies of field trials.
Traditional culture-dependent microbial methods are applied by researchers to isolate microbes from oil reservoirs and identify their potential functions to MEOR. However, the procedures to enrich and isolate microbes are complex, in most of cases, special media, special carbon resources and tens of incubations cycle during procedure of enrichment were needed. In addition, only a small percentage (less than 1%) (Amann et al., 1995) of viable microbes can be cultured on known nutrient media using the culture-dependent traditional techniques. Bacteria detected by traditional microbial methods are a minor part of the microbes inhabiting in oil reservoirs.
Recently, molecular microbial ecology represents a development in research methods, which contains utilizing techniques of molecular biology to investigate the ecology of microbes and offers new techniques to facilitate the detection of microbes. Researchers have investigated microbial diversity in samples collected from various oil reservoirs using culture-independent molecular biological methods.
Multiple groups of microorganisms with diverse phylogenetic affiliations have routinely been detected from oil reservoirs. However, an obscuring result from the studies based on culture-independent molecular techniques was that, in most of clone libraries, few to no clones or sequences detected were affiliated with the genus of Bacillus. These results insert an impression to us that Bacillus is rare or absent in these oil reservoirs.
When investigating microbial diversity in the original samples from oil reservoirs based on culture-independent molecular biological methods, DNA extraction from the spore-forming bacteria is more difficult than from other microbes, in addition, molecular biological methods is unable to detect a small proportion of 0.1-1% of bacteria (Head et al., 1998), both of which might be the major reasons for neglection of the group of Bacillus in clone libraries of samples from oil reservoirs.
The Bacillus is a group of Gram-positive, spore-forming bacteria, which is a potential microbial group for MEOR. How to detect and enrich the genus of Bacillus in samples from oil reservoirs is an urgent question faced by us. Considering the disadvantages and advantages of culture-dependent and culture-independent microbial methods and molecular biological methods, we provide a method to quickly detect the genus inhabiting in samples collected from oil reservoirs. This method is a combination of the advantages of both culture-dependent and culture-independent microbial methods and molecular biological methods.